[YaterSpoon]

Some drywall anchors are far better than others. I avoid the plastic plugs and screw-in "easy anchor" types.

Better are pop-toggles (but be sure to first "pop" them with the push tool.) Or togglers (but expensive), or old fashioned mollies, but it helps to have a Molly setter tool. The hammer-in neon green things are decent, too.

 

[YaterSpoon]

The issue is some of these attachment plates require "TINY" holes on the wall.

For example, look at this one by ATLAS LINEA, and it's not a cheap $20 bar, it's a $150 accessory set made in Italy.

The two mounting holes on the back plate is 3/8" apart. How can I even put in two drywall anchors 3/8" apart. If I drill two holes 1/4" apart for any anchor there would be almost no material left between the two holes.

Yeah, those are tough (ridiculous). Probably meant for plaster walls or where there's backer. How about surface-mounting a board, and then installing?

Or just use the anchors they came with. It's not your fault they purchased something so crazy. Let them know what to expect.

But..I might just use one molly and one #6 plastic nail-in anchor on each mounting plate. That'll fit.